with a vial and syringe. me, explaining what i was doing at breakfast and me discovering novolog mix 70/30 flexpen. flexpen is pre-filled with your pre-mix insulin. dial the exact dose. inject by pushing a button. no vials, syringes or coolers to carry. flexpen is insulin delivery my way. novolog mix 70/30 is an insulin used to control high blood sugar in adults with diabetes. do not inject if you do not plan to eat within 15 minutes to avoid low blood sugar. tell your healthcare provider about all medicines you take and all of your medical conditions, including if you are pregnant or breastfeeding. most common side effects include reactions at the injection site, weight gain, swelling of your hands and feet, and vision changes. other serious side effects include low blood sugar and low potassium in your blood. get medical help right away if you experience serious allergic reactions, body rash, trouble with breathing, fast heartbeat, sweating, or if you feel faint.